In recent years, ink-jet printers have become rapidly widespread due to high-speed printing, low noise, high-definition printing, low cost and the like. In the ink-jet printer, an ink-jet head that discharges an appropriate amount of ink is provided. As the ink-jet head, for example, an ink-jet head is disclosed in patent document 1.
In the ink-jet head of patent document 1, a pressure chamber is formed in a substrate, and a diaphragm is formed on the substrate so as to cover the pressure chamber. On the diaphragm, a lower electrode, a piezoelectric member and an upper electrode are formed in this order. In this configuration, when voltage is applied to the upper electrode and the lower electrode, the expansion and contraction of the piezoelectric member cause piezoelectric distortion (piezoelectric displacement), and the diaphragm is bent and deformed. The bending and deformation of the diaphragm cause the pressure within the pressure chamber to be increased, and thus ink droplets are discharged from a nozzle.
Here, the upper electrode is drawn out together with the piezoelectric member from an area above the pressure chamber to an area above the side wall of the pressure chamber, and thus it is possible to energize the upper electrode above the pressure chamber. Moreover, the upper electrode is drawn out together with the piezoelectric member, and thus it is possible to easily draw out the upper electrode. The reason for this is as follows.
For example, when only the upper electrode is drawn out from the area above the pressure chamber, one way is to draw out the upper electrode from the upper surface of the piezoelectric member in the area above the pressure chamber closely along the side surface of the piezoelectric member. However, since the side surface of the piezoelectric member is substantially perpendicular to the upper surface, especially when the thickness of the piezoelectric member is large, it is difficult to adhere the metal material that is to be the upper electrode to the side surface of the piezoelectric member by evaporation or sputtering, with the result that it is difficult to draw the upper electrode over the step of the thickness of the piezoelectric member. On the other hand, in the configuration in which the upper electrode is drawn out together with the piezoelectric member, since the upper electrode is preferably formed only on the upper surface of the piezoelectric member, it is easy to form the upper electrode by evaporation or the like. In other words, since it is not necessary to form such an upper electrode as to extend over the step of the thickness of the piezoelectric member, it is easy to draw out the upper electrode.
However, as described above, in the configuration in which the upper electrode is drawn out together with the piezoelectric member, since the piezoelectric member is continuous over the area above the pressure chamber and the area above the side wall of the pressure chamber, as the piezoelectric member above the pressure chamber expands and contracts, a bending load is applied onto the vicinity of the boundary between the piezoelectric member above the pressure chamber and the piezoelectric member above the side wall of the pressure chamber, that is, the portion of the piezoelectric member located above the side wall surface of the pressure chamber, with the result that stress is concentrated in this portion. Hence, a crack is produced in the vicinity of the boundary in the piezoelectric member, and this causes the upper electrode to be broken. Since the piezoelectric displacement of the piezoelectric member above the pressure chamber is suppressed by the piezoelectric member above the side wall of the pressure chamber, it is impossible to avoid a decrease in piezoelectric displacement.
In this respect, in the ink-jet head of patent document 2, a space portion is provided between a diaphragm and a piezoelectric member in an area above the boundary surface between a pressure chamber and the side wall of the pressure chamber, and the piezoelectric member and an upper electrode are drawn out over the space portion. In this way, the stress concentration in the area above the boundary surface is avoided, and thus the upper electrode is prevented from being broken.